Android app crashes on network request

Question 1

Try this,

public class Activity_Currency_Converter extends DashBoardActivity {
    public int to;
    public int from;
    public String [] val;
    public String s;
    public Handler handler;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_currency_converter);
        Spinner s1 = (Spinner) findViewById(R.id.spinner1);
        Spinner s2 = (Spinner) findViewById(R.id.spinner2);
        ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(
                this, R.array.name, android.R.layout.simple_spinner_item);
        adapter.setDropDownViewResource(android.R.layout.select_dialog_singlechoice);
        val  = getResources().getStringArray(R.array.value);
        s1.setAdapter(adapter);
        s2.setAdapter(adapter);
        s1.setOnItemSelectedListener(new spinOne(1));
        s2.setOnItemSelectedListener(new spinOne(2));
        Button b = (Button) findViewById(R.id.button1);
        b.setOnClickListener(new OnClickListener(){
            public void onClick(View v) {
                TextView t = (TextView) findViewById(R.id.textView4);   
                if(from == to)
                {
                    Toast.makeText(getApplicationContext(), "Invalid", 4000).show();
                }
                else
                {                                       
                      new GetResponseData(t).execute();                              
                    }                                           
                }                               
        });
    }
    public String getJson(String url)throws ClientProtocolException, IOException {

        StringBuilder build = new StringBuilder();
        HttpClient client = new DefaultHttpClient();
        HttpGet httpGet = new HttpGet(url);
        HttpResponse response = client.execute(httpGet);
        HttpEntity entity = response.getEntity();
        InputStream content = entity.getContent();
        BufferedReader reader = new BufferedReader(new InputStreamReader(content));
        String con;
        while ((con = reader.readLine()) != null) {
                    build.append(con);
                }
        return build.toString();
    }
    private class spinOne implements OnItemSelectedListener
    {
        int ide;
        spinOne(int i)
        {
            ide =i;
        }
        public void onItemSelected(AdapterView<?> parent, View view,
                int index, long id) {
            if(ide == 1)
                from = index;
            else if(ide == 2)
                to = index;

        }

        public void onNothingSelected(AdapterView<?> arg0) {
            // TODO Auto-generated method stub  
        }

    }
    class GetResponseData extends AsyncTask<String, String, String> {
         private ProgressDialog dialog;
         private ArrayList<String> titleList;
         private TextView textView;

         public GetResponseData(TextView textView) {
             this.textView=textView;
        }

         @Override
         protected void onPreExecute() {
         super.onPreExecute();
         dialog = ProgressDialog.show(Activity_Currency_Converter.this, "", "Loading",
         false);
         }

         @Override
         protected String doInBackground(String... params) {

             try {
                 String s = getJson("http://query.yahooapis.com/v1/public/yql?q=select%20*%20from%20yahoo.finance.xchange%20where%20pair%20in%20(%22"+val[from]+val[to]+"%22)&format=json&diagnostics=true&env=store%3A%2F%2Fdatatables.org%2Falltableswithkeys&callback=");                       
                JSONObject jObj;
                jObj = new JSONObject(s);
                String exResult = jObj.getJSONObject("query").getJSONObject("results").getJSONObject("rate").getString("Rate");
               return exResult;
                } catch (JSONException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                    return null;
                }
                catch (ClientProtocolException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                    return null;
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                    return null;
                }                      




         }

         @Override
         protected void onPostExecute(String result) {
         super.onPostExecute(result);
         if (dialog != null)
             dialog.dismiss();
         if(result!=null)
         {
          textView.setText(result);
         }
         }

         }
}

Question 2

Use Asynchtask for performing Network related operations.. Chack this for more details NetworkOnMainThread and Asynchtask

Question 3

Make StringBuilder class level, create your ProgressDialog accordingly. Inside your getJSON method create an async task like this

new AsyncTask<Void, Void, Void>() {

        protected void onPreExecute() {
          //Your code
        }

        @Override
        protected Void doInBackground(Void... params) {
        StringBuilder build = new StringBuilder();
        HttpClient client = new DefaultHttpClient();
        HttpGet httpGet = new HttpGet(url);
        HttpResponse response = client.execute(httpGet);
        HttpEntity entity = response.getEntity();
        InputStream content = entity.getContent();
        BufferedReader reader = new BufferedReader(new InputStreamReader(content));
        String con;
        while ((con = reader.readLine()) != null) {
                    build.append(con);
                }
        return null;
        }

        protected void onPostExecute(Void result) {
          //Update UI from here
        }
      }.execute();

Question 4

Use AsyncTask as

class myAsyncTask extends AsyncTask<String[] ,String,String>
{
    String s=null;
    String output=null;
    JSONObject main;

    @Override
    protected void onPreExecute() 
    {   


    }

    @Override
    protected String doInBackground(String[]... val) {

        s = getJson("http://query.yahooapis.com/v1/public/yql?q=select%20*%20from%20yahoo.finance.xchange%20where%20pair%20in%20(%22"+val[from]+val[to]+"%22)&format=json&diagnostics=true&env=store%3A%2F%2Fdatatables.org%2Falltableswithkeys&callback=");                       
                    JSONObject jObj;
                    jObj = new JSONObject(s);
                    String exResult = jObj.getJSONObject("query").getJSONObject("results").getJSONObject("rate").getString("Rate");

        return exResult;
    }
    @Override
    protected void onPostExecute(String result) {
        super.onPostExecute(result);
        t.setText(result);
             }
}

and then call the following method from the 'else' block

new myAsyncTask().execute(val);

Question 5

The app crashes due to strict mode policy, insert below given lines before you send a request to service or connecting to network:

 ThreadPolicy tp = ThreadPolicy.LAX;
 StrictMode.setThreadPolicy(tp);

Hope it Helps you :)